A vehicle rear body structure according to conventional technologies is shown in FIG. 7 (see Japanese Unexamined Patent Application Publication No. 2002-29453). FIG. 7A is a perspective view of a joined portion between a rear wheel housing and a rear floor panel. FIG. 7B is a perspective view of a rear floor side extension. FIG. 7C is a longitudinal sectional view taken along line VIIB-VIIB of FIG. 7A.
As shown in FIG. 7, in a vehicle rear body structure disclosed in Japanese Unexamined Patent Application Publication No. 2002-29453, a rear floor side extension 1 is longitudinally and vertically enlarged and joined at its front edge 1a to a joining area of a mating flange 3 located at the rear side of a rear wheel housing outer panel 2a. Then, the rear floor side extension 1 thus mounted to the rear body side is joined breadthways to an upstanding wall 6a of the rear floor side panel 6 through a draught opening 5 (see FIG. 7C) of a rear fender panel 4 when installed to a rear floor assembly. The vehicle rear body structure disclosed in Japanese Unexamined Patent Application Publication No. 2002-29453 allows the use of an enlarged rear floor side extension without posing any problems in joining the rear floor side extension, thereby enhancing the reinforcement of the rear side section.
A joined portion A (see FIG. 7A) between a rear floor panel (rear floor side panel 6) and the rear side extension 1 is subjected to vertical, longitudinal, and lateral loads from a suspension input point (rear wheel housing 2). In addition, the joined portion A constitutes a lower end of a vehicle rear end and is located at a side end corner, greatly affecting the stiffness of the vehicle rear section.
With this in mind, in a vehicle rear body structure disclosed in Japanese Unexamined Patent Application Publication No. 2002-29453, a slanted side H on the top end of a surface portion M formed between the joined portion A and a joined portion B (joined portion between the rear floor side extension 1 and the rear wheel housing 2) does not extend to the joined portion A from the joined portion B (see FIG. 7A), and thus contributes less to the stiffness of the vehicle rear section.
Also, in a vehicle rear body structure disclosed in Japanese Unexamined Patent Application Publication No. 2002-29453, the joined portion A and a joined portion C (joined portion between the rear floor side extension 1 and a body side panel) are vertically spaced apart from each other (see FIG. 7A) with only one plate member provided between the joined portion A and the joined portion C (see FIG. 7C), and thus contribute less to the stiffness of the vehicle rear section.
Furthermore, in a vehicle rear body structure disclosed in Japanese Unexamined Patent Application Publication No. 2002-29453, the rear floor panel 7 and the rear wheel housing 2 are joined to each other with two components, including the rear floor side panel 6 and the rear floor side extension 1, therebetween. A greater number of joined portions between such two components results in a lower contribution to the stiffness of the vehicle rear section.